Methods for determining the position of rotary parts of rotary drives of any kind, for example and in particular of rotors of electric machines, have been largely known and serve, for example in the case of certain electric machines, which generally can be regarded as synchronous machines and may be described, from the functional point of view, as sort of brushless d.c. motors--to mention only one preferred embodiment, although the present invention is by no means restricted to it--to excite certain predetermined coils for the purpose of generating corresponding magnetic fields so as to set the rotor of the machine into continuous rotation. It is understood that the respective coils are, therefore, excited in rapid succession and of course in a manner tuned to the desired rotary speed of the electric motor, it being, however, in any case indispensable to have at least relative knowledge of the rotary-angle position.
By "relative" it is to be understood in this connection that depending on the number of poles of the electric motor, certain structures will occur in repetition so that certain predetermined coils which are distributed over the stator part can be excited simultaneously.
However, there have also been known means for determining the position of rotary parts where an absolute position has to be determined, for example the upper dead center of internal combustion machines, because this angular position serves as reference for the injection times of diesel engines or for the entire ignition timing curve, depending on the operating mode of the internal-combustion machine. Such singular absolute positions can be determined by marks provided on a rotating wheel, including a toothed wheel, in which case an inductive approximation switch responds when an iron part forming this mark approaches the switch.
Considering, however, that great value is also placed on obtaining an actual-value signal for the rotary speed, in particular in connection with the determination of the rotor position of electric motors, tachogenerators have been known in the art in a broad range of forms, depending on the requirements placed on their accuracy. Such tachogenerators may, for example, take the form of incremental-value pickups, Hall generators or optoelectric means responding to the passage of rotary parts covering them.
According to another possibility, rotary speeds of rotary parts are determined by counting tooth-like projections arranged at the periphery of a rotary part, for example the teeth of the clutch ring of an internal combustion engine, in which case the respective speed may be represented in the form of a pulse sequence or of a corresponding counter reading.
Usually, and in most cases necessarily, such tachogenerators have associated to them a plurality of additional processing circuit components which serve, for example, for linearizing, amplifying or preparing the signals so obtained for further processing, for example for speed regulation. This is necessary because the useful level gained is very low in most of the cases and one cannot, therefore, do without such supplementary electronic means.
Now, it is the object of the present invention to provide quite generally a device for determining the rotary-angle position of rotary drives, preferably improved by the addition of supplementary means for recording the rotary speed (tachogenerator), which is of simple design and provides an image of the rotor position in the form of an analogue curve the shape of which can be determined at desire.
Considering that the present invention finds its practical implementation preferably in connection with a tachogenerator, where the driven magnet rotor and flat coils picking up the magnetic field emanating from the rotor are arranged in axial layers, it should be noted that it already has been known in a different context, in connection with an inductor for rotary electric machines (AT-PS 219 701) to build up a stationary magnet system and a rotor supplying rotary energy in axial layers in which case flat windings and laminar conductors are arranged on the rotor. Due to the arrangement in axial layers, a plane air gap is obtained between the rotor and the stator parts. The stator part comprises a plurality of permanent magnets each of which is connected in parallel, via a common yoke, to a magnetic subsidiary circuit comprising an electric excitation winding. The parallel subsidiary circuits, therefore, contribute very specially towards generating the inductor flux of the machine when the excitation winding is excited, while a magnetic short-circuit is produced for the respective permanent magnet of the stator part when the excitation winding is interrupted. There do not exist any relationships to the present invention.